TWI626514B - Metrology method and lithographic method, lithographic cell and computer program - Google Patents

Abstract

The invention discloses a method for measuring a target, an associated lithography method and a lithography unit. The method includes measuring, after exposing a structure by a lithography process, the target in a current layer on one of the substrates above the one or more previous layers, wherein the one or more previous layers each have undergone an etching step, The target is only included in at least one of the one or more previous layers. In this way, one post-etching measurement of the target is obtained.

Description

Weights and measures method and lithography method, lithography unit and computer program

The present invention relates to metrology methods and apparatus useful for device fabrication, for example, by lithography, and to methods of fabricating devices using lithography.

A lithography apparatus is a machine that applies a desired pattern onto a substrate, typically applied to a target portion of the substrate. The lithography apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that case, a patterning device (which is alternatively referred to as a reticle or pleated reticle) can be used to create a circuit pattern to be formed on individual layers of the IC. This pattern can be transferred to a target portion (eg, including portions of a die, a die, or several dies) on a substrate (eg, a germanium wafer). Transfer of the pattern is typically performed via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of sequentially adjacent adjacent target portions. In lithography procedures, the resulting structure needs to be measured frequently, for example, for program control and verification. Various tools for performing such measurements are known, including scanning electron microscopes that are often used to measure critical dimensions (CD), and for measuring overlays (alignment accuracy of two layers in the device) Specialization tool for measurement). The superposition can be described in terms of the degree of misalignment between the two layers, for example, a reference to a 1 nm cross-stacked pair can describe the case where the two layers are misaligned by up to 1 nm. Recently, various forms of scatterometers have been developed for use in the field of lithography. These devices direct the radiation beam onto the target and measure one or more properties of the scattered radiation - for example, the intensity at a single angle of reflection as a function of wavelength; the intensity at one or more wavelengths depending on the angle of reflection Or polarization based on the angle of reflection - to obtain a "spectrum" of the attribute of interest for the target. The determination of the attribute of interest can be performed by various techniques: for example, re-construction of objects by means of rigorous coupled wave analysis or a finite element method; library search; and principal component analysis. A relatively large (e.g., 40 micron by 40 micron) grating is used by conventional scatterometers, and the measuring beam produces a spot that is smaller than the grating (i.e., insufficient grating fill). This situation simplifies the mathematical re-construction of the goal because it can be considered infinite. However, in order to reduce the size of the target, for example, to 10 microns by 10 microns or less (for example) so that it can be positioned in the product features rather than in the scribe line, it has been proposed to make the grating smaller than the spot (ie, , the grating is overfilled). These targets are typically measured using dark field scatter measurements, where zero order diffraction (corresponding to specular reflection) is blocked and only high order is processed. Examples of dark field weights and measures can be found in the international patent applications WO 2009/078708 and WO 2009/106279, the entire contents of each of which are hereby incorporated by reference. Further developments of this technology have been described in the patent publications US Pat. No. 1,201,0,0,0, 704, A, US Pat. The contents of all such applications are also incorporated herein by reference. A pair of diffraction-based overlays using dark-field detection of the diffraction order enables stack-to-measurement of smaller targets. These targets can be smaller than the illumination spot and can be surrounded by the product structure on the wafer. A target can include multiple rasters that can be measured in one image. In known weights and measures techniques, by measuring the overlay target twice under certain conditions, simultaneously rotating the overlay target or changing the illumination mode or imaging mode to separately obtain the -1 ^st and +1 ^st diffraction order intensities. Obtain the stacking measurement results. The measurement of the target asymmetry (i.e., the asymmetry in the target) is provided with respect to the intensity asymmetry of the given stack versus the target (the comparison of the intensity of the diffraction orders). This asymmetry in the overlay pair can be used as an indicator of the overlay error (improper misalignment of the two layers). In recent years, integrated weights and measures have been designed. This includes in-line measurements of parameters (eg, overlays, focus or critical dimensions) on the substrate during the lithography procedure. It would be desirable to improve the accuracy of such measurements.

In a first aspect, the present invention provides a method of measuring a target, comprising: measuring a current layer on one of a substrate above one or more previous layers after exposing the structure by a lithography process The object, wherein the one or more previous layers each have undergone an etching step, and wherein the target is included only in at least one of the one or more previous layers, thereby obtaining an etch after etching the target Measure. In a second aspect, the present invention provides a method of performing a lithography process, comprising: performing a lithography step to form a structure in one or more previous layers on a substrate, at least of the previous layers One comprising a target; performing an etching step on the one or more previous layers; exposing one of the one or more previous layers above the previous layer; and after such steps: measuring the target to obtain one of the targets Measured after etching. In a third aspect, the present invention provides a lithography unit comprising a lithography apparatus and a metrology apparatus, the lithography unit operable to perform the first aspect or the second aspect of the method . The invention further provides a computer program comprising processor readable instructions, when executed on a device controlled by a suitable processor, causing the device controlled by the processor to perform the first aspect or the second state The method; and a computer program carrier including the computer program. The device controlled by the processor can include the lithography unit of the third aspect. Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail herein. It should be noted that the invention is not limited to the specific embodiments described herein. These embodiments are presented herein for illustrative purposes only. Additional embodiments will be apparent to those skilled in the art in view of the teachings herein.

Before describing the embodiments of the present invention in detail, it is intended to present an example environment in which embodiments of the invention may be practiced. Figure 1 shows the lithography apparatus LA as part of an industrial facility implementing a high capacity lithography manufacturing process at 200. In this example, the fabrication process is adapted for fabrication of a semiconductor product (integrated circuit) on a substrate such as a semiconductor wafer. Those skilled in the art will appreciate that a wide variety of products can be manufactured by processing different types of substrates with variations of this procedure. The production of semiconductor products is purely used as an example of today's commercial significance. Within the lithography apparatus (or simply "lithography tool 200"), the metro station MEA is shown at 202 and the exposure station EXP is shown at 204. Control unit LACU is shown at 206. In this example, each substrate is visited by a station and an exposure station to have an applied pattern. For example, in an optical lithography apparatus, a projection system is used to transfer a product pattern from a patterning device MA onto a substrate using an adjusted radiation and projection system. This transfer is accomplished by forming an image of the pattern in the layer of radiation-sensitive resist material.

The term "projection system" as used herein shall be interpreted broadly to encompass any type of projection system suitable for the exposure radiation used or for other factors such as the use of a immersion liquid or the use of a vacuum, including refraction, Reflective, catadioptric, magnetic, electromagnetic, and electrostatic optical systems, or any combination thereof. The patterning device MA can be a reticle or pleated reticle that imparts a pattern to a radiation beam that is transmitted or reflected by the patterning device. Well-known operating modes include step mode and scan mode. As is known, projection systems can cooperate with supports and positioning systems for substrates and patterning devices in a variety of ways to apply a desired pattern across a substrate to a plurality of target portions. A programmable patterning device can be used instead of a reticle with a fixed pattern. Radiation, for example, may include electromagnetic radiation in deep ultraviolet (DUV) or extreme ultraviolet (EUV) bands. The invention is also applicable to other types of lithography procedures, such as embossing lithography and direct writing lithography, for example, by electron beam.

The lithography apparatus control unit LACU controls all movements and measurements of various actuators and sensors for accommodating the substrate W and the reticle MA and performing the patterning operation. The LACU also includes signal processing and data processing capabilities to perform the calculations associated with the operation of the device. In effect, the control unit LACU will be implemented as a system of many sub-units that each handle real-time data acquisition, processing and control of subsystems or components within the device.

Prior to applying the pattern to the substrate at the exposure station EXP, the substrate is processed at the metrology station MEA so that various preliminary steps can be performed. The preliminary steps can include using a level sensor to map the surface height of the substrate, and using an alignment sensor to measure the position of the alignment marks on the substrate. The alignment marks are nominally configured in a regular grid pattern. However, the mark deviates from the ideal grid due to the inaccuracy of the mark and also due to the deformation of the substrate through its processing. Therefore, in addition to measuring the position and orientation of the substrate, the alignment sensor must actually measure in detail the position of many of the marks across the substrate area (where the device will print the product features at the correct location with extremely high accuracy) In case). The device can be of the so-called dual stage type with two substrate stages, each having a positioning system controlled by the control unit LACU. While exposing one substrate on one substrate stage at the exposure station EXP, another substrate can be loaded onto another substrate stage at the measurement station MEA, so that various preliminary steps can be performed. Therefore, the measurement of the alignment marks is extremely time consuming, and providing two substrate stages results in a substantial increase in the yield of the device. If the position sensor IF is unable to measure the position of the substrate table while the substrate stage is at the measurement station and at the exposure station, a second position sensor can be provided to enable tracking of the position of the substrate table at both stations. The lithography apparatus LA may, for example, belong to the so-called dual stage type, which has two substrate stages and two stations - an exposure station and a measuring station - between which the substrate stages can be exchanged. In the production facility, the device 200 forms part of a "lithography unit" or "micro-shadow cluster" which also contains a coating device 208 for the photosensitive resist and Other coatings are applied to the substrate W for patterning by the device 200. At the output side of device 200, a bake device 210 and a developing device 212 are provided for developing the exposed pattern into a solid resist pattern. Between all such devices, the substrate handling system is responsible for supporting the substrate and transferring the substrate from one piece of equipment to the next. The equipment, often collectively referred to as a coating development system, is under the control of a coating and developing system control unit. The coating development system control unit itself is controlled by the supervisory control system SCS, and the supervisory control system SCS is also micro-controlled. The photographic device control unit LACU controls the lithography device. Therefore, different devices can be operated to maximize yield and processing efficiency. The supervisory control system SCS receives the recipe information R, which provides a detailed definition of the steps to be performed to produce each patterned substrate. Once the pattern has been applied and developed in the lithography unit, the patterned substrate 220 is transferred to other processing devices (such as the processing devices illustrated at 222, 224, 226). A wide range of processing steps are performed by various devices in a typical manufacturing facility. For the sake of example, device 222 in this embodiment is an etch station and device 224 performs a post-etch annealing step. Further physical and/or chemical processing steps are applied to additional equipment 226 or the like. Numerous types of operations may be required to fabricate actual devices, such as deposition of materials, modification of surface material properties (oxidation, doping, ion implantation, etc.), chemical mechanical polishing (CMP), and the like. In fact, device 226 can represent a series of different processing steps performed in one or more devices. It is well known that the fabrication of semiconductor devices involves many iterations of this process to build device structures with appropriate materials and patterns layer by layer on the substrate. Thus, the substrate 230 that reaches the lithography cluster can be a newly prepared substrate, or it can be a substrate that has been previously completely processed in this cluster or in another device. Similarly, depending on the desired processing, the substrate 232 on the exit device 226 can be returned for subsequent patterning operations in the same lithography cluster, which can be designated for patterning operations in different clusters, or It can be a finished product to be sent for cutting and packaging. Each layer of the product structure requires a different set of program steps, and the equipment 226 for each layer can be completely different in type. Moreover, even where the processing steps to be applied by device 226 are nominally the same in a larger facility, there may be several machines that operate in parallel to perform several assumptions of step 226 on different substrates. Small differences or malfunctions in settings between such machines may mean that they affect different substrates in different ways. Even for relatively common steps for each layer, such as etching (device 222) may be performed by several etching devices that are nominally identical but operate in parallel to maximize yield. Moreover, in practice, the different layers require different etching procedures depending on the details of the material to be etched, for example, chemical etching, plasma etching, and require special requirements such as anisotropic etching. Previous and/or subsequent procedures (as just mentioned) may be performed in other lithography devices, and previous and/or subsequent procedures may be performed even in different types of lithography devices. For example, some of the layers in the device fabrication process that are extremely demanding on parameters such as resolution and overlays can be implemented in more advanced lithography tools than other layers that are less demanding. Therefore, some layers can be exposed to the infiltration type lithography tool while the other layers are exposed to the "dry" tool. Some layers can be exposed to tools that operate at DUV wavelengths, while others are exposed using EUV wavelength radiation. In order to properly and consistently expose the substrate exposed by the lithography apparatus, it is necessary to detect the exposed substrate to measure properties such as overlay error between subsequent layers, line thickness, critical dimension (CD), and the like. Thus, a manufacturing facility positioned with a lithography unit LC may also include one or more metrology systems. The metrology system can include a stand-alone metrology device MET 240 and/or an integrated metrology device IM 207. The stand-alone metrology device MET 240 houses some or all of the substrates W that have been processed in the lithography unit for offline measurement. The integrated metrology apparatus IM 207 performs in-line metrology and is integrated into the coating development system to receive and measure some or all of the substrate W immediately after exposure. The weights and measures results are provided directly or indirectly to a supervisory control system (SCS) 238. If an error is detected, the exposure of the subsequent substrate can be adjusted, especially if the metrology can be performed quickly and quickly enough that other substrates of the same batch are still to be exposed. A common example of a metrology device in a modern lithography production facility is a scatterometer, such as an angular resolution scatterometer or a spectral scatterometer, and which can be typically applied to the properties of the developed substrate at 220 before etching in device 222. . Where stand-alone metrology apparatus 240 and/or integrated metrology apparatus 207 are used, it can be determined that important performance parameters, such as overlay or critical dimension (CD), do not meet the specified accuracy requirements in the developed resist. Prior to the etching step, there is a chance of stripping the developed resist via the lithography cluster and reprocessing the substrate 220. As is also well known, by the supervisory control system SCS and/or the control unit LACU 206 making small adjustments over time, the metrology results 242 from the device 240 can be used to maintain the accurate performance of the patterning operation in the lithography cluster, thereby Minimize the risk of producing unqualified products and requiring heavy work. Of course, the metrology apparatus 240 and/or other metrology equipment (not shown) can be applied to measure the properties of the processed substrates 232, 234 and the lead-in substrate 230.

The metrology device is shown in Figure 2(a). The stand-alone metrology device 240 and/or the integrated metrology device 207 can include, for example, this metrology device or any other suitable metrology device. The target T and the diffracted radiation used to illuminate the target's measured radiation are illustrated in more detail in (b) of FIG. The illustrated metrology equipment is of the type known as dark field metrology equipment. The metrology device can be a stand-alone device or can be incorporated in, for example, a lithography device LA at the metrology station or in a lithography unit LC. The optical axis through which the device has several branches is represented by a dotted line O. In this apparatus, light emitted by a source 11 (e.g., a xenon lamp) is directed to a substrate W by an optical system including lenses 12, 14 and an objective lens 16 via a beam splitter 15. These lenses are arranged in a double sequence of 4F configurations. Different lens configurations can be used with the constraint that the lens configuration still provides the substrate image onto the detector while allowing access to the intermediate pupil plane for spatial frequency filtering. Thus, the range of angles at which radiation is incident on the substrate can be selected by defining a spatial intensity distribution in a plane that presents the spatial spectrum of the substrate plane (referred to herein as a (conjugate) pupil plane). In particular, this selection can be made by inserting a suitable form of aperture plate 13 between lenses 12 and 14 in the plane facing away from the projection image of the objective pupil plane. In the illustrated example, the aperture plates 13 have different forms (labeled 13N and 13S) allowing for different illumination modes to be selected. The illumination system in this example forms an off-axis illumination mode. In the first illumination mode, the aperture plate 13N provides off-axis illumination in a direction designated "north" for purposes of description only. In the second illumination mode, the aperture plate 13S is used to provide similar illumination, but provides illumination from the opposite direction labeled "South." Other lighting modes are possible by using different apertures. The rest of the pupil plane is ideally dark, because any unwanted light outside the desired illumination mode will interfere with the desired measurement signal. As shown in (b) of FIG. 2, the target T is placed with the substrate W perpendicular to the optical axis O of the objective lens 16. The substrate W may be supported by a support (not shown). The measuring radiation ray I incident on the target T at an angle to the axis O causes a zero-order ray (solid line 0) and two first-order ray (dot chain line +1 and double-point chain line -1). It should be borne in mind that in the case of the use of overfilled small targets, such rays are only one of many parallel rays covering the substrate area including the metrology target T and other features. Since the aperture in the plate 13 has a finite width (necessary for receiving a quantity of light), the incident ray I will actually occupy an angular range, and the diffracted rays 0 and +1/-1 will be slightly spread apart. According to the point spread function of the small target, each order +1 and -1 will spread further across the range of angles instead of a single ideal ray as shown. It should be noted that the grating pitch and illumination angle of the target can be designed or adjusted such that a step ray entering the objective lens is closely aligned with the central optical axis. The rays illustrated in (a) and 3 (b) of Fig. 2 are shown to be slightly off-axis to be purely distinguishable from the figure. At least the 0th order and the +1st order of the target T diffraction on the substrate W are collected by the objective lens 16 and guided back through the beam splitter 15. Returning to (a) of Figure 2, both the first and second illumination modes are illustrated by designating the exact opposite apertures labeled North (N) and South (S). When the incident ray I of the equivalent radiation is from the north side of the optical axis (i.e., when the first illumination mode is applied using the aperture plate 13N), the +1 diffracted ray labeled +1 (N) enters the objective lens 16. In contrast, when the second illumination mode is applied using the aperture plate 13S, the -1 diffracted ray (labeled -1(S)) is the diffracted ray entering the lens 16. The second beam splitter 17 divides the diffracted beam into two measuring branches. In the first measurement branch, the optical system 18 forms a diffraction spectrum of the target on the first sensor 19 (eg, a CCD or CMOS sensor) using a zero-order diffracted beam and a first-order diffracted beam (light)瞳 Planar image). One of the different points on the sensor in each diffraction step allows the image processing to compare and compare several orders. The pupil plane image captured by the sensor 19 can be used to focus the metrology device and/or normalize the intensity measurement of the first order beam. The pupil plane image can also be used for many measurement purposes such as re-construction. In the second measurement branch, the optical system 20, 22 forms an image of the target T on the sensor 23 (eg, a CCD or CMOS sensor). In the second measuring branch, an aperture stop 21 is provided in a plane conjugate to the pupil plane. The aperture stop 21 is used to block the zero-order diffracted beam such that the image of the target formed on the sensor 23 is formed only by a -1 or +1 first-order beam. The images captured by sensors 19 and 23 are output to a processor PU that processes the images, and the functionality of processor PU will depend on the particular type of measurement being performed. It should be noted that the term "image" is used herein in a broad sense. Therefore, if only one of the -1st order and the +1st order exists, the image of the raster line will not be formed. The particular form of aperture plate 13 and field stop 21 shown in Figure 2 is purely an example. In another embodiment of the invention, the target coaxial illumination is used and an aperture stop having an off-axis aperture is used to deliver substantially only one first order diffracted light to the sensor. In still other embodiments, instead of or in addition to the first order beam, a second order beam, a third order beam, and a higher order beam (not shown in Figure 2) may be used in the measurement. In order for the measurement radiation to be suitable for these different types of measurements, the aperture plate 13 can include a plurality of aperture patterns formed around the disk that rotate to bring the desired pattern into position. It should be noted that the aperture plate 13N or 13S may only be used to measure a grating oriented in one direction (X or Y depending on the setting). In order to measure the orthogonal grating, a target rotation of up to 90° and 270° can be performed. Numerous other variations and applications of the use of such aperture plates and apparatus are described in the previously published applications mentioned above. In the above, it is mentioned that the metrology is usually performed immediately after the development step and before the etching, wherein the overlay target is measured in the resist ("post-development" overlay measurement), especially when using an integrated metrology device When measuring in the line. This is because the post-etch measurement ("post-etch" stack-to-measure) will require an additional independent measurement step, which is time consuming in terms of time. Thus, the feedback control loop of the lithography program is based on post-development overlay measurement rather than post-etch overlay measurement. In addition, it can be shown that the post-etch measurement and the post-development measurement for the same target can be different. The actual associated stack is a post-etch stack, which is due to the removal of the resist during the etching step. This inconsistency between post-etch measurement and post-development measurement is largely due to the effect of the etching step on the target or due to stress relief after removal of the hard mask by the etching process. In addition, there is a significant greater distance (measured after development) between the gratings forming the unetched stack and the target compared to after etching (which can be observed in Figure 3). The effect of the gratings that are closer together after etching is to improve the signal coupling from the grating by the improved quality of the measurement quality. Figure 3 schematically illustrates three steps of a method of performing an post-etch metric that does not require an additional independent measurement step. In an embodiment, the method includes measuring a previous stack of etched and (as appropriate) (after development) the current stack pair during the formation of the current lithography layer; ie, above layer L _n and layer L _{n - 1} During the formation of the layer L _{n + 1} : (a) a pair of pairs from buried objects (a stack of layers between the layer L _n and the layer L _{n - 1} ) (b) a stack of pairs from the current layer ( Between layer L _{n + 1} and layer L _n ). This method performs measurement using an integrated metrology (eg, a metrology device integrated into a coating development system of a lithography unit). Such measurements are typically performed in-line immediately after the development step but before the etching step during processing of the substrate. Such measurements can be performed simultaneously with the pre-processing of the substrate (eg, resist coating, etc.) during the lithography process and thus take up very little extra time or take up extra time. Figure 3 shows the three steps of the lithography program (alone as part of a longer program). The first block shows a portion of the substrate after the first lithography step Li _n , wherein the layer L _n is exposed to a layer L _n-1 that has been formed and processed (developed and etched). After show development (i.e., pre-etching), the resist layer L _n of the mask layer over the structure and the material layer M1 _n M2 _n, L _n layer will eventually be etched into the material layer M2 _n after the etching step. In this particular example, layer _Ln-1 includes a stacked pair of gratings OVn _-1 and a product resolution paired pair of beams DOVn _-1 . In this particular example, layer L _n includes a first stack of gratings OV _n,1 (which is directly exposed over the stack of gratings OV _n-1 in layer L _n-1 , thereby forming a pair of targets), second Overlap grating OV _n,2 , product resolution overlay raster DOV _n (which is directly exposed above the product resolution in layer L _n-1 over the raster DOV _n-1 , thereby forming a product resolution overlay target) And critical dimension target CD _n . The second block shows the substrate after the etching step Ei _n . The third block shows the substrate after the second lithography step Li _n+1 , wherein the layer L _n+1 is exposed to the layer L _n and the layer L _n+1 . The developed (i.e., pre-etched) layer _{Ln+1 is shown} as a resist structure over the mask layer M1 _n+1 and the material layer M2 _n+1 , and the layer L _n+1 will eventually be etched after the etching step. To the material layer M2 _n+1 . In this particular example, layer L _n+1 is shown to include a first stack of gratings OV _n+1,1 (which is directly exposed over the stack of gratings OV _n,2 in layer L _n , thereby forming a stack Target) and the second stack of gratings OV _n+1,2 . Forming a second stack of gratings OV _{n+1, 2} to provide a lower constituent grating of the pair of targets for measuring the overlap between layer L _n+1 and subsequent layers and thus in the absence of subsequent layers This second stack of gratings is not necessary.

The first lithography step Li _n schematically indicates the measurement of the developed post-stacked target formed by the stacked gratings OV _n-1 , OV _{n, 1} to obtain a developed stack between the layer L _n and the layer L _n-1 For measuring OV _D n,n-1. The CD target CD _n is also measured to obtain a CD measurement CD _D n after development. These post-development overlays and/or CD measurements are used in control loop FB _D n for controlling the lithography step Li _n to subsequent substrates. This post-development control loop FB _D n is well known in integrated metrology systems. Other types of targets may also be included in this layer, such as focus targets for measuring focus. In the case where L _n layer comprises a focus target, the focus target may be measured after development and used for controlling the micro-Li _n subsequent fixing step of the substrate, as described in the control loop. The second lithography step of Li _{n + 1} measurement is schematically indicated by the stack grating OV _{n -} after etching _1, OV _{n, 1} is formed of the laminate with the layer L _n L _n to obtain the target _- between etch ₁ The back stack measures OV _E n,n-1. The present inventors have devised can be measured after the lithography step during Li _{n + 1} after the etching performed for the pretreatment step of this lithography step. Thus, during the formation of the layer L _{n + 1} (i.e., immediately after the development layer L _{n + 1} ), via the thin film mask layer M1 _{n + 1} and the material layer M2 _{n + 1} under the thin film mask layer After the etch of the two previous layers is performed, the measurement OV _E n,n-1, the layer L _{n + 1} will be etched into the material layer M2 _{n + 1} . Similarly, the CD can be measured L _n CD _E n L _n layer and the layer after the etching of layer L _n during this step _- after the etching products between _a resolution of the overlay measurement DOV _E n, n-1 It can be the same as the focus measurement after etching in the presence of the focus target in the layer L _n . Product resolution overlay versus weights will be described in more detail below. Further, as illustrated, layers may perform more conventional L _{n + 1} and between the post-development layer L _n of overlay metrology OV _D n + 1, n. Post-etch overlay measurement OV _E n,n-1, post-etch product resolution stack measurement DOV _E n,n-1 and/or post-etch CD measurement CD _E n can then be used in control loop FB _E n for controlling the micro-substrate Movies subsequent step of Li _n overlay and / or CD. The post-development overlay measurement OV _D n+1,n can be used in the control loop FB _D n+1 for controlling the lithography step Li _{n + 1} to the subsequent substrate. It is known that there may be inconsistencies between the stack-to-measure performed on a typical stack-to-target (including a grating having a pitch of about 500 nm) and the actual overlay of the product structure at product resolution. This inconsistency can result in an offset between the measured overlay value from the overlay target and the actual overlay of the product structure. The reason why the stack has a large pitch for the grating makes it possible to measure the overlap target (i.e., post-development measurement) in the resist. It is impossible to perform post-development measurement on the grating by the product resolution stack. This is because the small pitch (coupling with the distance between the grating when the upper grating is in the resist) means that there is no measurable first order. The signal, while the zeroth order signal is unstable at this distance. The method disclosed herein produces a product resolution overlay raster DOV _n , DOV _n-1 that can be measured to obtain a measure of product resolution overlay. For example, the product resolution grating can be a grating having a distance of less than 100 nanometers (eg, between 40 nanometers and 80 nanometers). This is because the stack-to-target can be measured after etching and therefore will now only contain small distances between the constituent gratings DOV _n , DOV _n-1 . This makes it possible to measure the zero-order signal with a sufficiently accurate measure. It should be noted that such post-etch measurements can be performed directly on the product structure, rather than on dedicated overlay gratings (this also applies to CD measurements). Thus, the term "target" should be understood to include the structure of the product.

It is possible to use a product resolution stack instead of a target, a larger pitch overlay target, but this would mean that the product resolution stack is not available for post-development measurement and control loops. Alternatively, the product resolution overlay can be used with the target in combination with a larger spacing stack. For example, the offset between the larger spaced overlay target and the overlay from the product resolution overlay to the target is likely to be determined and used to correct for subsequent measurements of the larger pitch overlay target. In this embodiment, the product resolution stack can be measured against the target (measured in-line on the integrated metrology device or separately measured on a single-machine metrology device) and the offset can be determined and used to improve as described herein And the accuracy of the measurement and measurement of the standard stack to the target. For example, this offset can be determined on a per-layer combination, on each substrate, or on a batch basis, as appropriate.

It should be appreciated that the concepts described herein are not limited to any one or combination of types of measurements (eg, overlays or CDs) or types of targets. The principle of post-etch measurement of the targets formed in one or more previous layers performed during the lithography process that forms the subsequent layers is critical. The target may include one of the overlay target, the product resolution overlay target, the focus target, and/or the CD target, or any combination. One or more targets may be two or more measurement type targets that may be used for different types of measurements on a single target. Such targets can be used for either or more of stacking measurements, product resolution overlays, focus measurements, and/or CD measurements.

Different layers may contain different combinations of different types of targets (or their constituent structures). For example, in an embodiment, the offset between the post-etch measurement and the post-development measurement can be determined and used to correct subsequent post-development measurements, thereby removing post-etch measurements in each condition. need. For example, this offset can be determined on a per layer (or layer combination) basis, on each substrate, or on a batch basis, as appropriate. While the above described objects are specifically designed and formed for metrology purposes for measurement purposes, in other embodiments, an attribute measurement can be performed on the target of the functional portion of the device formed on the substrate. Many devices have a regular grating-like structure. The terms "target raster" and "target" as used herein do not need to have specifically provided structure for the measurements performed. Furthermore, the distance P between the metrology targets is close to the resolution limit of the optical system of the scatterometer, but can be much larger than the typical product features produced by the lithography program in the target portion C. In practice, the lines and/or spaces of the stack within the target can be fabricated to include smaller structures that are similar in size to the product features. In association with a physical raster structure as embodied on a substrate and a patterned device, an embodiment can include a computer program containing one or more sequences of machine readable instructions describing a measurement substrate The above objectives and/or analytical measurements to obtain information about the lithography program. This computer program can be executed, for example, in the unit PU in the device of FIG. 3 and/or in the control unit LACU of FIG. A data storage medium (for example, a semiconductor memory, a magnetic disk or a compact disc) in which the computer program is stored may also be provided. In the case where an existing metrology device (eg, a metrology device of the type shown in FIG. 3) is already in production and/or in use, the updated computer program product can be supplied for causing the processor to perform the modified step S6. The present invention is therefore practiced by calculating stacking errors or other parameters that are less sensitive to structural asymmetry. The program may optionally be configured to control the optical system, substrate support, and the like to perform steps S2 through S5 for measuring asymmetry with respect to a suitable plurality of targets. Although the embodiments disclosed above are described in terms of a diffraction-based overlay measurement (eg, using a second measurement branch of the apparatus shown in FIG. 3(a)), in principle, The same model can be used for pupil-based overlay measurement (eg, using the first measurement branch of the device shown in Figure 3(a)). Therefore, it should be understood that the concepts described herein are equally applicable to diffraction-based stack-to-measurement and pupil-based stack-to-measurement. Although the use of embodiments of the present invention in the context of the content of optical lithography may be specifically referenced above, it will be appreciated that the invention may be used in other applications (eg, imprint lithography) and where the context of the content allows The next is not limited to optical lithography. In imprint lithography, the topography in the patterning device defines the pattern produced on the substrate. The patterning device can be configured to be pressed into a resist layer that is supplied to the substrate where the resist is cured by application of electromagnetic radiation, heat, pressure, or a combination thereof. After the resist is cured, the patterning device is removed from the resist to leave a pattern therein. The terms "radiation" and "beam" as used herein encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (eg, having or being about 365 nm, 355 nm, 248 nm, 193 nm, 157 nm or 126 nm wavelength) and extreme ultraviolet (EUV) radiation (eg, having a wavelength in the range of 5 nm to 20 nm); and a particle beam (such as an ion beam or an electron beam). The term "lens", as the context of the context permits, may refer to any or a combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic, and electrostatic optical components. The following items may be further described using the following items: 1. A method of measuring a target, comprising: measuring one of a substrate on one of the one or more previous layers after exposing the structure by a lithography process The target in the layer, wherein the one or more previous layers each have undergone an etching step, and wherein the target is included only in at least one of the one or more previous layers, thereby obtaining one of the targets Measured after etching.

2. The method of clause 1, wherein the measuring step is performed after a developing step of the current layer.

3. The method of clause 1 or 2, wherein the measuring step is performed through the current layer to be etched to the layer and/or a mask layer prior to etching the current layer.

4. The method of any preceding clause, wherein the target comprises measuring a stack of pairs of the first layer between the first layer and the second layer of the previous layers, The stack of pairs includes a first structure in the first layer and a second structure overlying the first structure in the second layer.

5. The method of clause 4, wherein the first structure and the second structure each have a resolution of less than 100 nanometers.

6. The method of clause 5, wherein the method comprises additionally measuring a structure comprising a resolution having a resolution greater than 100 nm and also including a stack of targets in the first layer and the second layer; An offset between the measurement of the overlay target comprising a structure having a resolution of less than 100 nm and the measurement of the overlay target comprising a structure having a resolution greater than 100 nm And using the offset to correct subsequent post-etch measurements of the overlay target comprising a structure having a resolution greater than 100 nanometers.

7. The method of any preceding clause, wherein the target comprises one of the previous levels of the critical dimension target for measuring a critical dimension in the layer.

8. The method of any preceding clause, wherein the method comprises forming the target Performing an initial measurement of the target before performing an etching step on the uppermost layer; determining an offset between the initial measurement of the target and the post-etching measurement of the target; and using the bias The shifting corrects the subsequent measurements of the targets performed prior to performing an etch step on the uppermost layer in which the target is formed.

9. The method of any preceding clause, comprising using the post-etching measurement to control formation of one of the appropriate one or more previous layers corresponding to the (identical) layer in which the target on the subsequent substrate is formed. Shadow program.

10. The method of any preceding clause, comprising performing the post-etching measurement during pre-processing of one or more subsequent substrates.

11. The method of any preceding clause, comprising: measuring, in a single measurement cycle having the post-etch measurement, an unprocessed target formed at least partially in the current layer to obtain the One of the processing targets is measured; and the measurement of the unprocessed target is used to control the formation of one of the current layers of the lithography process on the subsequent substrate.

12. The method of any preceding clause, wherein the target comprises one of the focus layers of one of the previous layers for measuring a focus in the layer.

13. A method of performing a lithography process, comprising: performing a lithography step to form a structure in one or more previous layers on a substrate, at least one of the prior layers comprising a target; Or performing an etch step on the plurality of previous layers; exposing one of the current layers above the one or more previous layers; and after such steps: measuring the target to obtain an etched measurement of one of the targets.

14. The method of clause 13, comprising performing a development step on the substrate between the exposing step and the measuring step to develop the current layer.

15. The method of clause 13 or 14, wherein the measuring step is performed through the current layer to be etched to the layer and/or a mask layer prior to etching the current layer.

The method of any one of clauses 13 to 15, wherein the object comprises measuring a stack between one of the first layers and one of the second layers of the previous layers A stack of objects, the stack of objects comprising a first structure in the first layer and a second structure overlying the first structure in the second layer.

17. The method of clause 16, wherein the first structure and the second structure each have a resolution of less than 100 nanometers.

18. The method of clause 17, wherein the method comprises additionally measuring a structure comprising a resolution having a resolution greater than 100 nm and also comprising a stack of targets within the first layer and the second layer; An offset between the measurement of the overlay target comprising a structure having a resolution of less than 100 nm and the measurement of the overlay target comprising a structure having a resolution greater than 100 nm And using the offset to correct for subsequent post-etch measurements of the overlay target comprising a structure having a resolution greater than 100 nanometers.

The method of any one of clauses 13 to 18, wherein the target comprises one of the prior levels of the critical dimension target for measuring a critical dimension in the layer.

The method of any one of clauses 13 to 19, wherein the target comprises one of the focus layers of one of the previous layers for measuring a focus in the layer.

The method of any one of clauses 13 to 20, wherein the method comprises performing an initial one of the targets during the formation of the target and before performing an etching step on the uppermost layer in which the target is formed Measuring; determining an offset between the initial measurement of the target and the post-etch measurement of the target; and using the offset to correct an etch performed on the uppermost layer in which the target is formed Subsequent measurements of these targets performed prior to the step. 22. The method of any one of clauses 13 to 21, wherein the post-etching measurement is used to form the appropriate one or more previous layers of the (identical) layer formed in the target corresponding to the subsequent substrate. Control the lithography program. 23. The method of any of clauses 13 to 22, comprising performing the post-etching measurement during pre-processing of one or more subsequent substrates. The method of any one of clauses 13 to 23, comprising performing, at least in part, on the current layer in parallel with the post-etch measurements of the target formed in the one or more previous layers Measuring one of the unprocessed targets; and using the measurements of the unprocessed target to control the lithography process when the current layer is formed on a subsequent substrate. 25. A computer program comprising processor readable instructions which, when run on a device controlled by a suitable processor, cause the device controlled by the processor to perform the method of any of the preceding clauses. 26. A computer program carrier comprising a computer program as set forth in clause 25. 27. A lithography unit comprising a lithography apparatus and a metrology apparatus, the lithography unit operable to perform the method of any one of clauses 1 to 24. 28. The lithography unit of clause 27, wherein the metrology apparatus comprises: an illumination system configured to illuminate to illuminate a combined target on the substrate using the lithography program; A system configured to detect scattered radiation resulting from illumination of the combined target. 29. The lithography unit of clause 27 or 28, wherein the lithography apparatus comprises: an illumination optical system configured to illuminate a pattern; a projection optical system configured to project an image of the pattern to On a substrate. The foregoing description of the specific embodiments will thus fully disclose the general nature of the invention, and the invention can be applied to various applications by applying the knowledge of the skill of the art without departing from the general inventive concept. It is easy to modify and/or adapt these particular embodiments without undue experimentation. Therefore, the adaptations and modifications are intended to be within the meaning and scope of the equivalents of the disclosed embodiments. It is understood that the phraseology or terminology herein is used for the purposes of the description The breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but only by the scope of the following claims and their equivalents.

0‧‧‧Diffractive ray/zero-order ray

+1‧‧‧Diffraction ray/first order ray

-1‧‧‧Diffraction rays/first-order rays

+1 (N) ‧ ‧ +1 diffracted ray

-1(S)‧‧‧-1 diffracted ray

11‧‧‧ source

12‧‧‧ lens

13‧‧‧Aperture plate

13N‧‧‧ aperture plate

13S‧‧‧Aperture plate

14‧‧‧ lens

15‧‧‧beam splitter

16‧‧‧ Objective lens/lens

17‧‧‧Second beam splitter

18‧‧‧Optical system

19‧‧‧First sensor

20‧‧‧Optical system

21‧‧‧Aperture stop/field stop

22‧‧‧Optical system

23‧‧‧ Sensors

200‧‧‧ lithography tools/equipment

202‧‧‧Measurement station

204‧‧‧Exposure station

206‧‧‧Control unit

207‧‧‧Integrated weighing and measuring equipment

208‧‧‧ Coating equipment

210‧‧‧ baking equipment

212‧‧‧Developing equipment

220‧‧‧ patterned substrate/substrate

222‧‧‧ Equipment/etching station

224‧‧‧ Equipment

226‧‧‧ Equipment/Steps

230‧‧‧Substrate/introduction substrate

232‧‧‧Processed substrate

234‧‧‧Processed substrate

240‧‧‧Single weight measurement equipment

242‧‧‧Measurement results

CD _D n‧‧‧ Critical dimension (CD) measurement after development

CD _E n‧‧‧ Critical dimension (CD) measurement after etching

CD _n ‧‧‧critical size (CD) target

DOV _E n,n-1‧‧‧After etching, product resolution overlay measurement

DOV _n ‧‧‧ product resolution overlay grating

DOV _{n - 1} ‧‧‧ product resolution overlay grating

Ei _n ‧‧‧ etching step

FB _D n‧‧‧Control loop

FB _D n+1‧‧‧ control loop

FB _E n‧‧‧Control loop

I‧‧‧Measured radiation/incident radiation

L _{n - 1} ‧ ‧ layer

L _n ‧‧ layer

L _{n + 1} ‧‧‧

Li _n ‧‧‧First lithography step

Li _{n + 1} ‧‧‧second lithography step

MA‧‧‧patterning device / doubling mask

M1 _n ‧‧‧mask layer

M1 _{n + 1} ‧‧‧mask layer

M2 _n ‧‧‧ material layer

M2 _{n + 1} ‧‧‧ material layer

OV _D n,n-1‧‧‧Development measurement after development

OV _D n+1,n‧‧‧Development measurement

OV _E n,n-1‧‧‧After etching

OV _{n - 1} ‧ ‧ stack pair grating

OV _{n , 1} ‧ ‧ first stack of gratings

OV _{n , 2} ‧‧‧Second stack of gratings

OV _{n + 1 , 1} ‧‧‧ first stack of gratings

OV _{n + 1 , 2} ‧‧‧second stack of gratings

O‧‧‧ optical axis

PU‧‧‧ processor/unit

R‧‧‧Formulation Information

SCS‧‧‧Supervisory Control System

T‧‧‧Metrics target

W‧‧‧Substrate

Embodiments of the present invention will now be described, by way of example only, with reference to the drawings in which: FIG. 1 depicts a lithographic apparatus along with other apparatus forming a production facility for a semiconductor device; FIG. 2 includes (a a schematic diagram of a dark field scatterometer for use with a first pair of illumination aperture measurement targets, (b) a detail of a diffraction spectrum of a target grating for a given illumination direction; FIG. 3 schematically depicts an embodiment in accordance with the present invention The three steps of the lithography program.

Claims (15)

A method of measuring a target, comprising: measuring a target after exposing a current layer on a substrate by a lithography process, wherein the substrate further comprises one or more preceding layers, Each has undergone an etch step, and wherein the target is only included in the one or more previous layers, thereby obtaining an etched measurement of one of the targets. The method of claim 1, wherein the measuring step is performed after a developing step of the current layer. The method of claim 1, wherein the measuring step is performed through the current layer to be etched to the layer and/or a mask layer prior to etching the current layer. The method of claim 1, wherein the target comprises a stack of pairs of targets between the first layer of the previous layers and the second layer of the previous layers, the overlay The target includes a first structure in the first layer and a second structure overlying the first structure in the second layer. The method of claim 4, wherein the first structure and the second structure each have a resolution of less than 100 nm, and wherein the method includes additionally measuring a structure having a resolution greater than 100 nm and a stack of targets included in the first layer and the second layer; determining the amount of the pair of targets comprising a structure having a resolution of less than 100 nm Measuring an offset between the measurement of the overlay target comprising a structure having a resolution greater than 100 nanometers; and using the offset to correct a resolution having a resolution greater than 100 nanometers The stack of structures is measured after subsequent etching of the target. The method of claim 1, wherein the target comprises one of the previous levels of the critical dimension target for measuring a critical dimension in the layer. The method of claim 1, wherein the method comprises performing an initial measurement of the target before performing an etching step on the uppermost layer in which the target is formed; determining the initial measurement of the target and the target An offset between the post-etch measurements; and the offset is used to correct subsequent measurements of the targets performed prior to performing an etch step on the uppermost layer in which the target is formed. A method of claim 1, comprising using the post-etch measurement to control forming a lithography program of the appropriate one or more previous layers corresponding to the (or) layer of the target formed on the subsequent substrate. The method of claim 1, comprising performing the post-etching measurement during pre-processing of one or more subsequent substrates. The method of claim 1, comprising: Measuring an unprocessed target formed at least partially in the current layer in a single measurement cycle having the post-etch measurement to obtain one of the unprocessed targets; and using the This measurement of the processed target controls the formation of one of the current layers of the lithography process on the subsequent substrate. The method of claim 1, wherein the target includes one of the focus layers of one of the previous layers for measuring a focus in the layer. A method of performing a lithography process, comprising: performing a lithography step to form a structure in one or more previous layers on a substrate, at least one of the prior layers comprising a target; The previous layer performs an etching step; exposing one of the current layers above the one or more previous layers; and after such steps: measuring the target to obtain an etched measurement of one of the targets. The method of claim 12, comprising performing, in parallel with the post-etching measurements on the target forming the one or more previous layers, at least partially forming an unprocessed target in the current layer Measuring; and using the measurements of the unprocessed target to control the lithography process when the current layer is formed on a subsequent substrate. A computer program comprising processor readable instructions that, when run on a device controlled by a suitable processor, cause the device controlled by the processor to perform the method of claim 1 law. A lithography unit comprising a lithography device and a metrology device, the lithography unit being operative to perform the method of claim 1.